I don't know what to say. Youassertthat the graphs of and are not perpendicular but they clearly are! The two lines intersect where which is the same as or . That is, the two lines intersect at . Now, when x= 2, y= 2x- 2 gives y= 4- 2= 2 so (2, 2) is a another point on the graph of y= 2x- 2.. When x= 0, gives y= 1 so (0, 1) is another point on .

That is, , (2, 2) and (0, 1) form a triangle with points on those two lines. The distance from (6/5, 2/5) to (2, 2) is . The distance from (6/5, 2/5) to (0, 1) is . The distance from (2, 2) to (0, 1) is . But now we see that . That is, the Pythagorean theorem holds- this is a right triangle with hypotenuse the line between (2, 2) and (0, 1). That proves that the intersectionisa right triangle.

Perhaps your "squares" aren't true squares and you are "stretching" one way more than the other.

Rereading your post- "The scales I'm using are such that ten small squares on my graph paper represent 1 unit on the x-axis and 2 units on the y-axis", that is exactly what you are doing! If one your x axis is stretched more than your y axis, you certainly are not representing angles correctly. Redraw the graph using ten small squares representing 1 unit on both axes or representing 2 units on both axes.